A climatic chamber essentially serves for regulating temperature and humidity. Although a coordinate measuring machine is accommodated in a climatic chamber, variations of the air pressure still influence the measurement result of the interferometers determining the position of the measurement objective and the measurement table with respect to a coordinate system. The influence of pressure variations of the ambient pressure is not attenuated by the climatic chamber.
A measuring device for measuring structures on wafers and/or masks is disclosed in the lecture script “Pattern Placement Metrology for Mask Making” by Dr. Carola Bläsing. The lecture was given on the occasion of the Semicon conference, Education Program, in Geneva on Mar. 31, 1998. It describes a coordinate measuring machine in detail. It also mentions that the coordinate measuring machine is accommodated in a climatic chamber regulating the temperature <±0.01° C. and the humidity to <±1% of relative humidity. It also discloses a laser interferometer with which the position of the measurement table within the X/Y plane may be determined. An etalon is used for determining the variations of temperature and humidity.
German patent DE 196 28 969 also discloses a coordinate measuring device and also discusses the problems caused by climatic air pressure changes and air humidity changes, also after opening doors of the climatic chamber, and thus influencing the wavelength of the light used for obtaining measurement results. In order to solve these problems, a double-beam interferometer with effectively reduced influence of the wavelength changes on the position measurement is disclosed. This is achieved by inserting a transparent, closed, incompressible body into the optical reference path or the optical measurement path so that the portions of the optical reference path and the optical measurement path located outside the body have the same length for a certain positioning of the movable measurement table. For this purpose, the measurement table is provided with a reflecting surface at a certain location.
U.S. Pat. No. 5,469,260 discusses the influence of fast, random air movements, such as they occur after opening or closing doors or after movements in the vicinity of the measuring device. The localized air pressure variations caused thereby result in local changes of the refractive index and thus wavelength changes in the light beam. The problem is suggested to be solved by casing the optical measurement and reference paths in tubes that are open at both ends. Air with a defined temperature stabilization or temperature-stabilized gas is to be blown into the tubes. Tubes with a telescope-like extension mechanism are suggested for the optical measurement path that is variable in length. By casing most of the light beam, the influence of fast air pressure variations is mostly prevented.
German published application DE 19949005 discloses a means and a method for introducing various transparent substrates into a high-precision measuring device. The system is accommodated in a climate-controlled chamber.
German published application DE 10 2005 052 757 A1 discloses a device for measuring the position of an object with a laser interferometer system. The at least one laser interferometer system is accommodated in a climate chamber together with the object. The climate chamber has air intake apertures in one area and several air exhaust apertures in another area. There are further provided means in the climate chamber to direct at least part of the flow through the climate chamber out of the area of the laser axes of the at least one laser interferometer system during operation. However, the document does not discuss the problems of measurement accuracy or reproducibility of the measurement results if they are influenced by pressure variations of the ambient air.
U.S. Pat. No. 6,267,131 discloses a method for controlling the pressure in a chamber. It discloses a method for controlling the pressure in a chamber, wherein the pressure is to be kept at a constant pressure in a chamber where the measurement with a laser is performed. The pressure level in the chamber is to exceed ambient pressure. For this purpose, the ambient air pressure is measured. A pressure level significantly above the transient pressure variations of the ambient air pressure is set. Air is introduced into the chamber to reach the predetermined pressure level.
U.S. Patent Application 2007/0085986 discloses an exposure device and a method for correcting the instrumentation of the exposure device. The air pressure in the exposure device is measured, and optical parameters, such as wavelength or lenses, are then set accordingly based on the measurement results to correct the error caused by the change in air pressure.
U.S. Pat. No. 6,580,087 discloses an inspection device. There are provided two blowers blowing a sufficient flow of cleaned air into the inspection device. However, this device does not serve for achieving a constant pressure level or a pressure level above ambient air pressure.
The article “First Measurement Data Obtained On The New Vistec LMS IPRO4”. Proc. of SPIE vol. 6533, no. 653301, 7 pages, January 2007, by Dieter Adam et al. discusses the problem of the reproducibility of measurements. It only discusses that temperature and humidity have to be much better controlled in the climatic chamber surrounding the measuring means.
Unfortunately, the previous prior art systems require complex systems or elements to eliminate the changes of the measurement wavelengths caused by air pressure variations.
FIG. 1 is a schematic drawing of a prior art coordinate measuring device Several coordinate measurement devices 1 of the type shown in FIG. 1 are known from prior art. For the sake of completeness, the operation and arrangement of the individual elements of the coordinate measuring device 1 are described. The coordinate measuring device 1 includes a measurement table 20 arranged to be movable on air bearings 21 in a plane 25a in the X-coordinate direction and in the Y-coordinate direction. The plane 25a is formed of an element 25. It is known to make element 25 of granite. The position of the measurement table 20 is measured by means of at least one laser interferometer 24 emitting a light beam 23 for the measurement. The element itself is positioned on vibration dampers 26 to thus keep building vibrations away from the measuring device.
Substrate 2 carrying the structures 3 to be measured is deposited on the measurement table 20. The substrate 2 may be illuminated with a transmitted light illumination means 6 and/or an incident light illumination means 14. The light of the transmitted light illumination means 6 reaches the substrate 2 via a deflecting mirror 7 and a condenser 8. Similarly, the light of the incident light illumination means 14 reaches the substrate 2 via a measurement objective 9. The measurement objective 9 is provided with an adjusting means 15 which allows adjusting the measurement objective 9 in the Z-coordinate direction. The measurement objective 9 collects the light coming from the substrate 2 and directs it out of the incident light illumination axis 5 by means of a partially transmitting deflecting mirror 12 and directs it to a camera 10 provided with a detector 11. The detector 11 is connected to a computer system 16 generating digital images from the measurement values determined by the detector 11.